diff --git a/lib/Epub/Epub.cpp b/lib/Epub/Epub.cpp
index 932f8b5..a9e501d 100644
--- a/lib/Epub/Epub.cpp
+++ b/lib/Epub/Epub.cpp
@@ -280,6 +280,8 @@ bool Epub::load(const bool buildIfMissing) {
   Serial.printf("[%lu] [EBP] Cache not found, building spine/TOC cache\n", millis());
   setupCacheDir();
 
+  const uint32_t indexingStart = millis();
+
   // Begin building cache - stream entries to disk immediately
   if (!bookMetadataCache->beginWrite()) {
     Serial.printf("[%lu] [EBP] Could not begin writing cache\n", millis());
@@ -287,6 +289,7 @@ bool Epub::load(const bool buildIfMissing) {
   }
 
   // OPF Pass
+  const uint32_t opfStart = millis();
   BookMetadataCache::BookMetadata bookMetadata;
   if (!bookMetadataCache->beginContentOpfPass()) {
     Serial.printf("[%lu] [EBP] Could not begin writing content.opf pass\n", millis());
@@ -300,8 +303,10 @@ bool Epub::load(const bool buildIfMissing) {
     Serial.printf("[%lu] [EBP] Could not end writing content.opf pass\n", millis());
     return false;
   }
+  Serial.printf("[%lu] [EBP] OPF pass completed in %lu ms\n", millis(), millis() - opfStart);
 
   // TOC Pass - try EPUB 3 nav first, fall back to NCX
+  const uint32_t tocStart = millis();
   if (!bookMetadataCache->beginTocPass()) {
     Serial.printf("[%lu] [EBP] Could not begin writing toc pass\n", millis());
     return false;
@@ -330,6 +335,7 @@ bool Epub::load(const bool buildIfMissing) {
     Serial.printf("[%lu] [EBP] Could not end writing toc pass\n", millis());
     return false;
   }
+  Serial.printf("[%lu] [EBP] TOC pass completed in %lu ms\n", millis(), millis() - tocStart);
 
   // Close the cache files
   if (!bookMetadataCache->endWrite()) {
@@ -338,10 +344,13 @@ bool Epub::load(const bool buildIfMissing) {
   }
 
   // Build final book.bin
+  const uint32_t buildStart = millis();
   if (!bookMetadataCache->buildBookBin(filepath, bookMetadata)) {
     Serial.printf("[%lu] [EBP] Could not update mappings and sizes\n", millis());
     return false;
   }
+  Serial.printf("[%lu] [EBP] buildBookBin completed in %lu ms\n", millis(), millis() - buildStart);
+  Serial.printf("[%lu] [EBP] Total indexing completed in %lu ms\n", millis(), millis() - indexingStart);
 
   if (!bookMetadataCache->cleanupTmpFiles()) {
     Serial.printf("[%lu] [EBP] Could not cleanup tmp files - ignoring\n", millis());
diff --git a/lib/Epub/Epub/BookMetadataCache.cpp b/lib/Epub/Epub/BookMetadataCache.cpp
index 98f86c1..8ba7c5b 100644
--- a/lib/Epub/Epub/BookMetadataCache.cpp
+++ b/lib/Epub/Epub/BookMetadataCache.cpp
@@ -40,7 +40,6 @@ bool BookMetadataCache::endContentOpfPass() {
 bool BookMetadataCache::beginTocPass() {
   Serial.printf("[%lu] [BMC] Beginning toc pass\n", millis());
 
-  // Open spine file for reading
   if (!SdMan.openFileForRead("BMC", cachePath + tmpSpineBinFile, spineFile)) {
     return false;
   }
@@ -49,12 +48,40 @@ bool BookMetadataCache::beginTocPass() {
     return false;
   }
 
+  if (spineCount >= LARGE_SPINE_THRESHOLD) {
+    spineHrefIndex.clear();
+    spineHrefIndex.reserve(spineCount);
+    spineFile.seek(0);
+    for (int i = 0; i < spineCount; i++) {
+      auto entry = readSpineEntry(spineFile);
+      SpineHrefIndexEntry idx;
+      idx.hrefHash = fnvHash64(entry.href);
+      idx.hrefLen = static_cast<uint16_t>(entry.href.size());
+      idx.spineIndex = static_cast<int16_t>(i);
+      spineHrefIndex.push_back(idx);
+    }
+    std::sort(spineHrefIndex.begin(), spineHrefIndex.end(),
+      [](const SpineHrefIndexEntry& a, const SpineHrefIndexEntry& b) {
+        return a.hrefHash < b.hrefHash || (a.hrefHash == b.hrefHash && a.hrefLen < b.hrefLen);
+      });
+    spineFile.seek(0);
+    useSpineHrefIndex = true;
+    Serial.printf("[%lu] [BMC] Using fast index for %d spine items\n", millis(), spineCount);
+  } else {
+    useSpineHrefIndex = false;
+  }
+
   return true;
 }
 
 bool BookMetadataCache::endTocPass() {
   tocFile.close();
   spineFile.close();
+
+  spineHrefIndex.clear();
+  spineHrefIndex.shrink_to_fit();
+  useSpineHrefIndex = false;
+
   return true;
 }
 
@@ -260,16 +287,37 @@ void BookMetadataCache::createTocEntry(const std::string& title, const std::stri
   }
 
   int16_t spineIndex = -1;
-  spineFile.seek(0);
-  for (int i = 0; i < spineCount; i++) {
-    auto spineEntry = readSpineEntry(spineFile);
-    if (spineEntry.href == href) {
-      spineIndex = static_cast<int16_t>(i);
+
+  if (useSpineHrefIndex) {
+    uint64_t targetHash = fnvHash64(href);
+    uint16_t targetLen = static_cast<uint16_t>(href.size());
+
+    auto it = std::lower_bound(spineHrefIndex.begin(), spineHrefIndex.end(),
+      SpineHrefIndexEntry{targetHash, targetLen, 0},
+      [](const SpineHrefIndexEntry& a, const SpineHrefIndexEntry& b) {
+        return a.hrefHash < b.hrefHash || (a.hrefHash == b.hrefHash && a.hrefLen < b.hrefLen);
+      });
+
+    while (it != spineHrefIndex.end() && it->hrefHash == targetHash && it->hrefLen == targetLen) {
+      spineIndex = it->spineIndex;
       break;
     }
-  }
-  if (spineIndex == -1) {
-    Serial.printf("[%lu] [BMC] addTocEntry: Could not find spine item for TOC href %s\n", millis(), href.c_str());
+
+    if (spineIndex == -1) {
+      Serial.printf("[%lu] [BMC] createTocEntry: Could not find spine item for TOC href %s\n", millis(), href.c_str());
+    }
+  } else {
+    spineFile.seek(0);
+    for (int i = 0; i < spineCount; i++) {
+      auto spineEntry = readSpineEntry(spineFile);
+      if (spineEntry.href == href) {
+        spineIndex = static_cast<int16_t>(i);
+        break;
+      }
+    }
+    if (spineIndex == -1) {
+      Serial.printf("[%lu] [BMC] createTocEntry: Could not find spine item for TOC href %s\n", millis(), href.c_str());
+    }
   }
 
   const TocEntry entry(title, href, anchor, level, spineIndex);
diff --git a/lib/Epub/Epub/BookMetadataCache.h b/lib/Epub/Epub/BookMetadataCache.h
index c7e9590..180f1b3 100644
--- a/lib/Epub/Epub/BookMetadataCache.h
+++ b/lib/Epub/Epub/BookMetadataCache.h
@@ -2,6 +2,7 @@
 
 #include <SDCardManager.h>
 
+#include <algorithm>
 #include <string>
 #include <vector>
 
@@ -55,6 +56,27 @@ class BookMetadataCache {
   FsFile spineFile;
   FsFile tocFile;
 
+  // Index for fast href→spineIndex lookup (used only for large EPUBs)
+  struct SpineHrefIndexEntry {
+    uint64_t hrefHash;    // FNV-1a 64-bit hash
+    uint16_t hrefLen;     // length for collision reduction
+    int16_t spineIndex;
+  };
+  std::vector<SpineHrefIndexEntry> spineHrefIndex;
+  bool useSpineHrefIndex = false;
+
+  static constexpr uint16_t LARGE_SPINE_THRESHOLD = 400;
+
+  // FNV-1a 64-bit hash function
+  static uint64_t fnvHash64(const std::string& s) {
+    uint64_t hash = 14695981039346656037ull;
+    for (char c : s) {
+      hash ^= static_cast<uint8_t>(c);
+      hash *= 1099511628211ull;
+    }
+    return hash;
+  }
+
   uint32_t writeSpineEntry(FsFile& file, const SpineEntry& entry) const;
   uint32_t writeTocEntry(FsFile& file, const TocEntry& entry) const;
   SpineEntry readSpineEntry(FsFile& file) const;
diff --git a/lib/Epub/Epub/parsers/ContentOpfParser.cpp b/lib/Epub/Epub/parsers/ContentOpfParser.cpp
index 3a63a30..4b64d7c 100644
--- a/lib/Epub/Epub/parsers/ContentOpfParser.cpp
+++ b/lib/Epub/Epub/parsers/ContentOpfParser.cpp
@@ -39,6 +39,9 @@ ContentOpfParser::~ContentOpfParser() {
   if (SdMan.exists((cachePath + itemCacheFile).c_str())) {
     SdMan.remove((cachePath + itemCacheFile).c_str());
   }
+  itemIndex.clear();
+  itemIndex.shrink_to_fit();
+  useItemIndex = false;
 }
 
 size_t ContentOpfParser::write(const uint8_t data) { return write(&data, 1); }
@@ -130,6 +133,16 @@ void XMLCALL ContentOpfParser::startElement(void* userData, const XML_Char* name
           "[%lu] [COF] Couldn't open temp items file for reading. This is probably going to be a fatal error.\n",
           millis());
     }
+    
+    // Sort item index for binary search if we have enough items
+    if (self->itemIndex.size() >= LARGE_SPINE_THRESHOLD) {
+      std::sort(self->itemIndex.begin(), self->itemIndex.end(),
+        [](const ItemIndexEntry& a, const ItemIndexEntry& b) {
+          return a.idHash < b.idHash || (a.idHash == b.idHash && a.idLen < b.idLen);
+        });
+      self->useItemIndex = true;
+      Serial.printf("[%lu] [COF] Using fast index for %zu manifest items\n", millis(), self->itemIndex.size());
+    }
     return;
   }
 
@@ -181,6 +194,15 @@ void XMLCALL ContentOpfParser::startElement(void* userData, const XML_Char* name
       }
     }
 
+    // Record index entry for fast lookup later
+    if (self->tempItemStore) {
+      ItemIndexEntry entry;
+      entry.idHash = fnvHash(itemId);
+      entry.idLen = static_cast<uint16_t>(itemId.size());
+      entry.fileOffset = static_cast<uint32_t>(self->tempItemStore.position());
+      self->itemIndex.push_back(entry);
+    }
+
     // Write items down to SD card
     serialization::writeString(self->tempItemStore, itemId);
     serialization::writeString(self->tempItemStore, href);
@@ -221,19 +243,50 @@ void XMLCALL ContentOpfParser::startElement(void* userData, const XML_Char* name
       for (int i = 0; atts[i]; i += 2) {
         if (strcmp(atts[i], "idref") == 0) {
           const std::string idref = atts[i + 1];
-          // Resolve the idref to href using items map
-          // TODO: This lookup is slow as need to scan through all items each time.
-          //       It can take up to 200ms per item when getting to 1500 items.
-          self->tempItemStore.seek(0);
-          std::string itemId;
           std::string href;
-          while (self->tempItemStore.available()) {
-            serialization::readString(self->tempItemStore, itemId);
-            serialization::readString(self->tempItemStore, href);
-            if (itemId == idref) {
-              self->cache->createSpineEntry(href);
-              break;
+          bool found = false;
+
+          if (self->useItemIndex) {
+            // Fast path: binary search
+            uint32_t targetHash = fnvHash(idref);
+            uint16_t targetLen = static_cast<uint16_t>(idref.size());
+
+            auto it = std::lower_bound(self->itemIndex.begin(), self->itemIndex.end(),
+              ItemIndexEntry{targetHash, targetLen, 0},
+              [](const ItemIndexEntry& a, const ItemIndexEntry& b) {
+                return a.idHash < b.idHash || (a.idHash == b.idHash && a.idLen < b.idLen);
+              });
+
+            // Check for match (may need to check a few due to hash collisions)
+            while (it != self->itemIndex.end() && it->idHash == targetHash) {
+              self->tempItemStore.seek(it->fileOffset);
+              std::string itemId;
+              serialization::readString(self->tempItemStore, itemId);
+              if (itemId == idref) {
+                serialization::readString(self->tempItemStore, href);
+                found = true;
+                break;
+              }
+              ++it;
             }
+          } else {
+            // Slow path: linear scan (for small manifests, keeps original behavior)
+            // TODO: This lookup is slow as need to scan through all items each time.
+            //       It can take up to 200ms per item when getting to 1500 items.
+            self->tempItemStore.seek(0);
+            std::string itemId;
+            while (self->tempItemStore.available()) {
+              serialization::readString(self->tempItemStore, itemId);
+              serialization::readString(self->tempItemStore, href);
+              if (itemId == idref) {
+                found = true;
+                break;
+              }
+            }
+          }
+
+          if (found && self->cache) {
+            self->cache->createSpineEntry(href);
           }
         }
       }
diff --git a/lib/Epub/Epub/parsers/ContentOpfParser.h b/lib/Epub/Epub/parsers/ContentOpfParser.h
index ce0039c..2e7e3a4 100644
--- a/lib/Epub/Epub/parsers/ContentOpfParser.h
+++ b/lib/Epub/Epub/parsers/ContentOpfParser.h
@@ -2,6 +2,7 @@
 #include <Print.h>
 
 #include <vector>
+#include <algorithm>
 
 #include "Epub.h"
 #include "expat.h"
@@ -30,6 +31,27 @@ class ContentOpfParser final : public Print {
   FsFile tempItemStore;
   std::string coverItemId;
 
+  // Index for fast idref→href lookup (used only for large EPUBs)
+  struct ItemIndexEntry {
+    uint32_t idHash;      // FNV-1a hash of itemId
+    uint16_t idLen;       // length for collision reduction
+    uint32_t fileOffset;  // offset in .items.bin
+  };
+  std::vector<ItemIndexEntry> itemIndex;
+  bool useItemIndex = false;
+
+  static constexpr uint16_t LARGE_SPINE_THRESHOLD = 400;
+
+  // FNV-1a hash function
+  static uint32_t fnvHash(const std::string& s) {
+    uint32_t hash = 2166136261u;
+    for (char c : s) {
+      hash ^= static_cast<uint8_t>(c);
+      hash *= 16777619u;
+    }
+    return hash;
+  }
+
   static void startElement(void* userData, const XML_Char* name, const XML_Char** atts);
   static void characterData(void* userData, const XML_Char* s, int len);
   static void endElement(void* userData, const XML_Char* name);
diff --git a/lib/ZipFile/ZipFile.cpp b/lib/ZipFile/ZipFile.cpp
index 2a97858..fec8b9f 100644
--- a/lib/ZipFile/ZipFile.cpp
+++ b/lib/ZipFile/ZipFile.cpp
@@ -74,6 +74,10 @@ bool ZipFile::loadAllFileStatSlims() {
     file.seekCur(m + k);
   }
 
+  // Set cursor to start of central directory for sequential access
+  lastCentralDirPos = zipDetails.centralDirOffset;
+  lastCentralDirPosValid = true;
+
   if (!wasOpen) {
     close();
   }
@@ -102,15 +106,35 @@ bool ZipFile::loadFileStatSlim(const char* filename, FileStatSlim* fileStat) {
     return false;
   }
 
-  file.seek(zipDetails.centralDirOffset);
+  // Phase 1: Try scanning from cursor position first
+  uint32_t startPos = lastCentralDirPosValid ? lastCentralDirPos : zipDetails.centralDirOffset;
+  uint32_t wrapPos = zipDetails.centralDirOffset;
+  bool wrapped = false;
+  bool found = false;
+
+  file.seek(startPos);
 
   uint32_t sig;
   char itemName[256];
-  bool found = false;
 
-  while (file.available()) {
-    file.read(&sig, 4);
-    if (sig != 0x02014b50) break;  // End of list
+  while (true) {
+    uint32_t entryStart = file.position();
+
+    if (file.read(&sig, 4) != 4 || sig != 0x02014b50) {
+      // End of central directory
+      if (!wrapped && lastCentralDirPosValid && startPos != zipDetails.centralDirOffset) {
+        // Wrap around to beginning
+        file.seek(zipDetails.centralDirOffset);
+        wrapped = true;
+        continue;
+      }
+      break;
+    }
+
+    // If we've wrapped and reached our start position, stop
+    if (wrapped && entryStart >= startPos) {
+      break;
+    }
 
     file.seekCur(6);
     file.read(&fileStat->method, 2);
@@ -123,15 +147,25 @@ bool ZipFile::loadFileStatSlim(const char* filename, FileStatSlim* fileStat) {
     file.read(&k, 2);
     file.seekCur(8);
     file.read(&fileStat->localHeaderOffset, 4);
-    file.read(itemName, nameLen);
-    itemName[nameLen] = '\0';
 
-    if (strcmp(itemName, filename) == 0) {
-      found = true;
-      break;
+    if (nameLen < 256) {
+      file.read(itemName, nameLen);
+      itemName[nameLen] = '\0';
+
+      if (strcmp(itemName, filename) == 0) {
+        // Found it! Update cursor to next entry
+        file.seekCur(m + k);
+        lastCentralDirPos = file.position();
+        lastCentralDirPosValid = true;
+        found = true;
+        break;
+      }
+    } else {
+      // Name too long, skip it
+      file.seekCur(nameLen);
     }
 
-    // Skip the rest of this entry (extra field + comment)
+    // Skip extra field + comment
     file.seekCur(m + k);
   }
 
@@ -253,6 +287,8 @@ bool ZipFile::close() {
   if (file) {
     file.close();
   }
+  lastCentralDirPos = 0;
+  lastCentralDirPosValid = false;
   return true;
 }
 
diff --git a/lib/ZipFile/ZipFile.h b/lib/ZipFile/ZipFile.h
index 0144ed4..b895881 100644
--- a/lib/ZipFile/ZipFile.h
+++ b/lib/ZipFile/ZipFile.h
@@ -25,6 +25,10 @@ class ZipFile {
   ZipDetails zipDetails = {0, 0, false};
   std::unordered_map<std::string, FileStatSlim> fileStatSlimCache;
 
+  // Cursor for sequential central-dir scanning optimization
+  uint32_t lastCentralDirPos = 0;
+  bool lastCentralDirPosValid = false;
+
   bool loadFileStatSlim(const char* filename, FileStatSlim* fileStat);
   long getDataOffset(const FileStatSlim& fileStat);
   bool loadZipDetails();